Package including a lidstock laminate

ABSTRACT

A method of forming a package by heat sealing a trap-printed laminate to a support member (e.g., tray). The laminate has a free shrink in each of the transverse and machine directions of at least about 10% at 200° F. and at least about 21% at 240° F. The laminate has an oxygen transmission rate of no more than about 100 cubic centimeters. The outside layer of the laminate comprises at least about 40% of one or more relatively high-melt polymers each having a melting point at least about 25° F. higher than the lowest melting point polymer of the sealant layer. The first film has an oxygen transmission rate greater than the oxygen transmission rate of the second film.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a packaging film, and moreparticularly to a laminate useful as a lidstock for sealing a trayclosed.

[0002] It is common in food packaging operations for a food product,such as fresh meat, to be placed on a tray, such as a thermoformedexpanded polystyrene tray having a central depressed area and asurrounding peripheral flange. A thermoplastic film or laminate may thenbe positioned over the food and heat sealed to the peripheral flange tohermetically enclose the food product. In such arrangement, thethermoplastic film or laminate is the “lid” or “lidstock” and the trayis a “support member.”

[0003] The lidstock should be capable of forming a strong, hermetic sealwith the support member. This is true even where the sealing area of thetray may be exposed or contaminated with by-product (e.g., meat purge)from the packaged food. This is also true where, as is commonly thecase, the support member is relatively rigid. Heat sealing a flexiblelidstock to a rigid support member is more challenging than heat sealingthe flexible lidstock to either another flexible film or laminate or toitself (for example, in a fin seal arrangement commonly used in verticalform-fill-seal operations).

[0004] To heat seal the lid to the support member, a heated bar engagesthe outside of the lid to compress it against the flange of the supportmember. In so doing, heat transfers from the heated bar to the outsideof the lid, through the thickness of the lid, to the inside sealantlayer of the lid, and to the flange of the support member. The resultingheat and compression causes the contacting surfaces of the lid andsupport member to become molten and to intermix with one another. Theheating bar is then removed to allow the sealed area to cool and form asealed bond.

[0005] The heat from the heat seal process may also cause aheat-shrinkable lidstock to shrink or create a shrink tension in theareas of the lidstock that have been exposed to a sufficient amount ofheat for a sufficient amount of time to effect a shrink.

[0006] The seal strength of the resulting sealed package may bedetermined by several methods. The support member may be pierced with aninflation needle and the interior of the sealed package may then beinflated until the lid or seal between the lid and support member fails.A higher internal inflation pressure at failure indicates a strongerseal strength. Alternatively, the sealed package may be placed in avacuum chamber and subjected to decreasing external pressures untilfailure—a lower external pressure at failure indicating a stronger sealstrength. Also, a representative sample of the seal may be cut from thesealed package (or formed separately) so that the lidstock may be pulledfrom the support member, for example, using an Instron tensile testerunder specified conditions. A higher maximum force attained beforefailure indicates a stronger seal strength.

[0007] In all of these tests of seal strength, the failure mechanism mayoccur in one or more of several ways. In each case, the failure modeseeks a failure path requiring the least amount of force. For example,the bond between the lidstock and the support member may fail adhesivelyso that the lidstock simply peels away from the support member. Or, thelidstock may fail cohesively along a path cutting generallyperpendicularly through one or more layers of the lidstock—and then failadhesively along the interface between two layers of the lidstock. Thefailure path may combine an intricate path of cohesive and adhesivefailures—all while the lidstock is being stretched by the appliedforce—to present a complicated failure mode.

[0008] The above discussion is made to establish that a weaker cohesivestrength within a layer of the lidstock and/or a weaker adhesive bondstrength between layers of the lidstock may weaken the seal strength ofthe sealed package. This is especially true where the seal strengthfailure mode is not simply the peeling of the lidstock from the supportmember by adhesive failure of the sealing bond between the lid and thesupport member.

[0009] A desirable lidstock provides gas (e.g., oxygen, carbon dioxide)barrier attributes sufficient to enhance the storage life of thepackaged food. The barrier characteristics of the lidstock may haveincreased importance where the interior atmosphere of the package may bemodified, for example, to decrease the concentration of oxygen from thatof ambient air or to increase the concentration of oxygen and carbondioxide from that of ambient air. For example, in packaging meat, theatmosphere in the sealed package may comprise about 80% by volume oxygenand about 20% by volume carbon dioxide in order to inhibit the growth ofharmful microorganisms and extend the time period in which the meatretains its attractive red (“bloom”) coloration. Oxygen and carbondioxide barrier attributes may be imparted to a film by incorporating,for example as a film layer, one or more resins having low permeabilityto oxygen. (Since carbon dioxide barrier properties generally correlatewith oxygen barrier properties, only oxygen barrier properties arediscussed in detail herein.)

[0010] It is not unusual for the inter-layer bond strengths associatedwith the incorporation of barrier resins or barrier layers into alidstock to be weaker than the inter-layer bond strengths that would bepresent if the barrier resin or layer were absent. That is to say, theinter-layer bond strength between a barrier layer and an adjacent layeris usually the weakest inter-layer bond strength of a film. It is alsopossible that weaker inter-layer bond strengths may be associated withone or more “tie layers” that may accompany the use of a barrier layer.Although a tie layer may be inserted between the barrier layer and anotherwise adjacent film layer in order to improve the inter-layer bondadhesion, the resulting bond strength between the tie layer and itsadjacent film layer may be less than the bond strength between the tielayer and its adjacent barrier layer. Accordingly, the tie layer maypresent the weakest inter-layer bond strength of the lidstock—and thuspresent the failure path during a seal strength test.

[0011] In order to produce packaged product at a fast (and thereforeeconomical) rate, the lidstock should be capable of being quickly heatsealed to the support member. A lidstock that facilitates quick heatsealing is said to have good “sealability.”

[0012] It is also desirable for the lidstock to be printed. Suchprinting provides important information to the end-user of the packagedfood—information such as the ingredients of the packaged food, thenutritional content, package opening instructions, food handling andpreparation instructions, and food storage instructions. The printingmay also provide a pleasing image and/or trademark or other advertisinginformation to enhance the retail sale of the packaged product.

[0013] Such printed information may be placed on the outside surface ofthe lidstock. However, such surface printing is directly exposed to aheated bar during the heat seal operation that seals the lid to thesupport member. As a result, the surface printing may become smeared orotherwise degraded. A surface printing is also exposed to other physicalabuses during distribution and display of the packaged product. Suchabuse may also degrade the clarity and presentation of the printedimage.

[0014] Once the lidstock has been sealed to a support member to form aclosed package, it is also desirable that the lidstock not appearwrinkled or wavy. Such wrinkles or waves tend to form in the cornerareas of a sealed lidstock—and may appear even if the sealed lidstockforms a tight, “drum-like” lid for the support member. The wrinkles mayalso appear as relatively small film corrugations near the sealed areaof the lid, in particular at the leading and trailing ends (relative tothe machine direction) of the package. Such wrinkles or waves cause thepackage to present a less than desirable appearance to the customer.

SUMMARY OF THE INVENTION

[0015] The present invention addresses one or more of the aforementionedproblems. A laminate is provided that comprises a first film having aninside surface and an outside surface opposite the inside surface of thefirst film. The first film comprises a sealant layer forming the insidesurface of the first film. The sealant layer comprises one or morepolymers each having a given melting point. At least one polymer of thesealant layer has the lowest melting point of the one or more polymersin the sealant layer. The laminate also comprises a second film havingan inside surface and an outside surface opposite the inside surface.The second film comprises an outside layer forming the outside surfaceof the second film. The outside layer comprises at least about 40% byweight of the outside layer of one or more relatively high-melt polymerseach having a melting point at least about 25° F. higher than the lowestmelting point polymer of the sealant layer. The laminate also includes aprinted image between the first and second films. The first film has anoxygen transmission rate greater than the oxygen transmission rate ofthe second film, measured (at standard temperature and pressure) persquare meter per day per 1 atmosphere of oxygen pressure differentialmeasured at 0% relative humidity and 23° C. The laminate has an oxygentransmission rate of no more than about 100 cubic centimeters (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C. The laminate has a free shrink in each of thetransverse and machine directions of at least about 10% at 200° F. andat least about 21% at 240° F. The laminate is heat sealed to a supportmember to form a closed package.

[0016] Heat sealing a laminate to a support member (e.g., tray) wherethe laminate has the recited free shrinks at both 200° F. and 240° F.reduces the amount and size of wrinkles (e.g., lid corrugations near thesealing area) and/or waves that may otherwise form in the lid of theresulting sealed package.

[0017] The laminate may provide enhanced seal strength relative tolaminates having a barrier layer as an inner layer of the sealant filmof the laminate. It is believed that a barrier layer often presents aweaker inter-layer bond strength relative to the inter-layer bondstrengths of the other layers. When a packaging seal fails, it istypically because of a delamination between layers having the weakestinter-layer bond strength within a film of the laminate.

[0018] By placing the barrier layer in the outside film of the laminate,the relatively weaker inter-layer bond strength may be positionedfarther from the bond between the laminate and the support member. Whensuch potential inter-layer failure is farther from the inside (i.e.,food-side) of the laminate, the failure tear propagation (i.e., the pathof inter-film cohesive failure) must travel farther to reach the“weakest link” inter-layer delamination path. This farther distance inthe present invention is believed to enhance the seal strength.

[0019] Further, the placement of barrier components in the outside filmof the laminate may allow for greater flexibility in manufacturing thelidstock laminate. This is because the inside sealant film may bemanufactured without the additional restriction associated withaccommodating barrier components in a coextruded, oriented film. Forexample, the extrusion of a barrier layer often requires highertemperatures than those needed to extrude the other layers of the film.This higher temperature associated with a barrier layer may limit theamount of lower melting point materials that can be used in thefilm—otherwise, the film may flow too easily and the melt strength maybe lowered to an unacceptable level for processing. Also, theorientation of a film having a barrier layer may require a higherorientation temperature, which can soften lower melting point materialsin the film to an unacceptable level, causing an unstable orientation orwelding together of adjacent layers. Thus, the incorporation of thebarrier components in the outside film allows greater choices inimparting the desired shrink and other attributes to the inside, sealantfilm of the laminate.

[0020] The laminate may incorporate a trap print arrangement, whichenhances the protection of the printed image of the laminate during theheat seal process that seals the laminate to a support member.

[0021] The laminate provides a low rate of oxygen transmission, whichenables the atmosphere within the sealed package to be modified toextend the shelf life and bloom “color life” of a packaged red meatproduct. The laminate also provides excellent print quality and opticalclarity.

[0022] The laminate can provide excellent sealability to a supportmember. This allows a packager to run the heat sealing machine at a fastrate while also providing good seal strength between the laminate andthe tray. The resulting seal between the laminate and the tray mayprovide excellent strength even where the seal is formed in the presenceof contaminants and under variable heat sealing temperatures.

[0023] These and other objects, advantages, and features of theinvention will be more readily understood and appreciated by referenceto the detailed description of the invention and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a perspective view of the sealed package of the presentinvention; and

[0025]FIG. 2 is a fragmentary, representational sectional view of theinventive laminate and sealed package of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The inventive laminate 10 comprises sealant film 12 laminated tobarrier film 14 to trap print image 16 between the sealant and barrierfilms. Sealant film 12 may be monolayer, two-layer, or have three ormore layers (as shown in FIG. 1). Also, barrier film 14 may bemonolayer, two-layer, or have three or more layers (as shown in FIG. 1).The laminate 10 may be sealed to support member 18 (e.g., a tray) toform sealed package 20 enclosing, for example, food product 22.

Sealant Film

[0027] The sealant film 12 defines an inside (i.e., food side) surface24 and an outside surface 26 opposite the inside surface. The polymermaterial (i.e., component or blend of components) that forms the insidesurface 24 of the sealant film has a melting point that facilitates heatsealing the laminate 10 to a support member 18. If the sealant film ismonolayer, then it may have the composition, attributes, and physicalcharacteristics as discussed in conjunction with the Sealant Layersection below.

[0028] The sealant film 12 may have any total thickness as long as itprovides the desired properties (e.g., flexibility, Young's modulus,optics, strength) for the given packaging application of expected use.The sealant film may have a thickness of less than about any of thefollowing: 10 mils, 5 mils, 4 mils, 3 mils, 2 mils, 1.5 mils, 1.4 mils,1.3 mils, 1.2 mils, 1.1 mils, and 1 mil. (A “mil” is equal to 0.001inch.) The sealant film may also have a thickness of at least about anyof the following: 0.3 mils, 0.4 mils, 0.5 mils, 0.6 mils, 0.7 mils, 0.75mils, 0.8 mils, 0.9 mils, 1 mil, 1.2 mil, 1.4 mil, and 1.5 mil. Thesealant film may have a thickness of at least about any of the followingpercentages of the thickness of the barrier film: 50%, 60%, 70%, 80%,90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, and 175%. For example,the thickness of the sealant film may be greater than or equal to thethickness of the barrier film.

[0029] The sealant film 12 may be relatively permeable to oxygenrelative to the barrier film 14 discussed below. For example, thesealant film 12 may have an oxygen transmission rate higher than that ofthe barrier film 14 by at least about any of the following: 50, 75, 100,200, 500, and 1,000 cubic centimeters (at standard temperature andpressure) per square meter per day per 1 atmosphere of oxygen pressuredifferential measured at 0% relative humidity and 23° C., measuredaccording to ASTM D-3985. Also, the sealant film 12 may have an oxygentransmission rate of at least about any of the following: 110, 200, 500,1,000, 2,000, 3,000, 5,000, 10,000, 15,000, 20,000, and 50,000 cubiccentimeters (at standard temperature and pressure) per square meter perday per 1 atmosphere of oxygen pressure differential measured at 0%relative humidity and 23° C., measured according to ASTM D-3985.

[0030] The sealant film 12 has a heat-shrinkable attribute. For example,the sealant film 12 may have a free shrink measured at 200° F. in atleast one direction (i.e., machine or transverse direction), in at leasteach of two directions (machine and transverse directions), or a totalfree shrink of at least about any of the following values: 5%, 7%, 10%,15%, 20%, 30%, 40%, 50%, and 60%. Also, sealant film 12 may have a freeshrink measured at 240° F. in at least one direction (machine ortransverse directions), in each of at least two directions (machine andtransverse directions), or a total free shrink measured of at leastabout any of the following values: 7%, 10%, 15%, 20%, 25%, 30%, 40%,50%, 55%, 60%, 65%, and 70%.

[0031] As is known in the art, the total free shrink is determined bysumming the percent free shrink in the machine (longitudinal) directionwith the percentage of free shrink in the transverse direction. Forexample, a film which exhibits 50% free shrink in the transversedirection and 40% free shrink in the machine direction has a total freeshrink of 90%.

[0032] Unless otherwise indicated, each reference to free shrink in thisapplication means a free shrink determined by measuring the percentdimensional change in a 10 cm×10 cm specimen when subjected to selectedheat (i.e., at a certain temperature exposure) according to ASTM D 2732.Also, a reference herein to the shrink attributes of a film that is acomponent of a laminate refers to the shrink attributes of the filmitself, which can be measured by separating the film from thelaminate—for example, by using an appropriate solvent to dissolve theadhesive that bonds the films together to form the laminate.

[0033] The sealant or first film 12 is preferably multilayer (i.e.,includes two or more layers) so that the layers in combination impartthe desired performance characteristics to the sealant film. The sealantfilm 12 may, for example, comprise from 2 to 15 layers, at least 3layers, at least 4 layers, at least 5 layers, from 2 to 4 layers, from 2to 5 layers, and from 5 to 9 layers. As used herein, the term “layer”refers to a discrete film component which is coextensive with the filmand has a substantially uniform composition.

[0034] A multilayer sealant film includes a sealant layer 28 forming thefood-side or inside surface and a skin or print-side layer 30 formingthe outside or non-food surface of the sealant film. The multilayersealant film may also include one or more additional layers 32, such ascore, bulk, and tie layers, although the sealant film may have acomposition such that tie layers are not incorporated in the sealantfilm.

[0035] Below are some examples of combinations in which the alphabeticalsymbols designate the resin layers. Where the multilayer sealant filmrepresentation below includes the same letter more than once, eachoccurrence of the letter may represent the same composition or adifferent composition within the class that performs a similar function.A/D, A/C/D, A/B/D, A/B/C/D, A/C/B/D, A/B/B/D, A/C/B/C/D, A/B/B/B/D,A/B/C/B/D, A/C/B/B/D, A/C/B/B/C/D, A/B/C/B/C/D, A/C/B/C/B/D,A/B/C/B/B/D, A/C/B/B/B/D, A/C/B/C/B/D, A/C/B/B/B/C/D

[0036] “A” is the sealant layer (heat seal layer), as discussed below.

[0037] “B” is a core or bulk layer, as discussed below.

[0038] “C” is a tie layer, as discussed below.

[0039] “D” is an skin or print-side layer, as discussed below.

Sealant Layer of the Sealant Film

[0040] Sealant layer 28 forms the inside surface 24 of the laminate 10.Sealant layer 28 facilitates the heat-sealing of laminate 10 to anotherobject, such as a support member or tray 18. The sealant layerpreferably includes selected components having a melt or softening pointlower than that of the components of the other layers of the sealantfilm. The sealant layer may comprise a resin having a Vicat softeningtemperature of less than about any of the following values: 120° C.,115° C., 110° C., 105° C., 100° C., 95° C., and 90° C. The sealant layermay include one or more polymers having a melt-flow index of at leastabout any of the following: 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2., 2.5, 2.8, 3,3.5, 4, 5, 6, 7, 8, 9, 10, 15, and 20. The sealant layer may include oneor more polymers having a melting point of less than about any of thefollowing: 130° C., 125° C., 120° C., 115° C., 112° C., 110° C., 108°C., 105° C., 103° C., 100° C., 98° C., and 95° C., in an amount of atleast about any of the following percentages (based on the weight of thesealant layer): 30, 40, 50, 60, 70, 80, 90, and100.

[0041] All references to “Vicat” values in this application are measuredaccording to ASTM 1525 (1 kg). All references to melt-flow index in thisapplication are measured according to ASTM D1238, at a temperature andpiston weight as specified according to the material as set forth in theASTM test method. All references to the melting point of a polymer orresin in this application refers to the melting peak temperature of thedominant melting phase of the polymer or resin as determined bydifferential scanning calorimetry according to ASTM D-3418.

[0042] The sealant layer may include one or more thermoplastic polymersincluding polyolefins, polystyrenes, polyurethanes, polyamides,polyesters, polyvinyl chlorides, and ionomers.

[0043] Useful polyolefins include ethylene homo- and co-polymers andpropylene homo- and co-polymers. Ethylene homopolymers include highdensity polyethylene (“HDPE”) and low density polyethylene (“LDPE”).Ethylene copolymers include ethylene/alpha-olefin copolymers (“EAOs”),ethylene/unsaturated ester copolymers, and ethylene/(meth)acrylic acid.(“Copolymer” as used in this application means a polymer derived fromtwo or more types of monomers, and includes terpolymers, etc.)

[0044] EAOs are copolymers of ethylene and one or more alpha-olefins,the copolymer having ethylene as the majority mole-percentage content.Preferably, the comonomer includes one or more C₃-C₂₀ α-olefins, morepreferably one or more C₄-C₁₂ α-olefins, and most preferably one or moreC₄-C₈ α-olefins. Particularly preferred α-olefins include 1-butene,1-hexene, 1-octene, and mixtures thereof.

[0045] EAOs include one or more of the following: 1) medium densitypolyethylene (“MDPE”), for example having a density of from 0.93 to 0.94g/cm3; 2) linear medium density polyethylene (“LMDPE”), for examplehaving a density of from 0.926 to 0.94 g/cm3; 3) linear low densitypolyethylene (“LLDPE”), for example having a density of from 0.915 to0.930 g/cm3; 4) very-low or ultra-low density polyethylene (“VLDPE” and“ULDPE”), for example having density below 0.915 g/cm3, and 5)homogeneous EAOs. Useful EAOs include those having a density of lessthan about any of the following: 0.925, 0.922, 0.92, 0.917, 0.915,0.912, 0.91, 0.907, 0.905, 0.903, 0.9, and 0.898 grams/cubic centimeter.Unless otherwise indicated, all densities herein are measured accordingto ASTM D1505.

[0046] The polyethylene polymers may be either heterogeneous orhomogeneous. As is known in the art, heterogeneous polymers have arelatively wide variation in molecular weight and compositiondistribution. Heterogeneous polymers may be prepared with, for example,conventional Ziegler Natta catalysts.

[0047] On the other hand, homogeneous polymers are typically preparedusing metallocene or other single site-type catalysts. Such single-sitecatalysts typically have only one type of catalytic site, which isbelieved to be the basis for the homogeneity of the polymers resultingfrom the polymerization. Homogeneous polymers are structurally differentfrom heterogeneous polymers in that homogeneous polymers exhibit arelatively even sequencing of comonomers within a chain, a mirroring ofsequence distribution in all chains, and a similarity of length of allchains. As a result, homogeneous polymers have relatively narrowmolecular weight and composition distributions. Examples of homogeneouspolymers include the metallocene-catalyzed linear homogeneousethylene/alpha-olefin copolymer resins available from the Exxon ChemicalCompany (Baytown, Tex.) under the EXACT trademark, linear homogeneousethylene/alpha-olefin copolymer resins available from the MitsuiPetrochemical Corporation under the TAFMER trademark, and long-chainbranched, metallocene-catalyzed homogeneous ethylene/alpha-olefincopolymer resins available from the Dow Chemical Company under theAFFINITY trademark.

[0048] Another useful ethylene copolymer is ethylene/unsaturated estercopolymer, which is the copolymer of ethylene and one or moreunsaturated ester monomers. Useful unsaturated esters include: 1) vinylesters of aliphatic carboxylic acids, where the esters have from 4 to 12carbon atoms, and 2) alkyl esters of acrylic or methacrylic acid(collectively, “alkyl (meth)acrylate”), where the esters have from 4 to12 carbon atoms.

[0049] Representative examples of the first (“vinyl ester”) group ofmonomers include vinyl acetate, vinyl propionate, vinyl hexanoate, andvinyl 2-ethylhexanoate. The vinyl ester monomer may have from 4 to 8carbon atoms, from 4 to 6 carbon atoms, from 4 to 5 carbon atoms, andpreferably 4 carbon atoms.

[0050] Representative examples of the second (“alkyl (meth)acrylate”)group of monomers include methyl acrylate, ethyl acrylate, isobutylacrylate, n-butyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate,methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, n-butylmethacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate. Thealkyl (meth)acrylate monomer may have from 4 to 8 carbon atoms, from 4to 6 carbon atoms, and preferably from 4 to 5 carbon atoms.

[0051] The unsaturated ester (i.e., vinyl ester or alkyl (meth)acrylate)comonomer content of the ethylene/unsaturated ester copolymer may rangefrom about 6 to about 18 weight %, and from about 8 to about 12 weight%, based on the weight of the copolymer. Useful ethylene contents of theethylene/unsaturated ester copolymer include the following amounts: atleast about 82 weight %, at least about 85 weight %, at least about 88weight %, no greater than about 94 weight %, no greater than about 93weight %, and no greater than about 92 weight %, based on the weight ofthe copolymer.

[0052] Representative examples of ethylene/unsaturated ester copolymersinclude ethylene/methyl acrylate, ethylene/methyl methacrylate,ethylene/ethyl acrylate, ethylene/ethyl methacrylate, ethylene/butylacrylate, ethylene/2-ethylhexyl methacrylate, and ethylene/vinylacetate.

[0053] Another useful ethylene copolymer is ethylene/(meth)acrylic acid,which is the copolymer of ethylene and acrylic acid, methacrylic acid,or both.

[0054] Useful propylene copolymer includes propylene/ethylene copolymers(“EPC”), which are copolymers of propylene and ethylene having amajority weight % content of propylene, such as those having an ethylenecomonomer content of less than 10%, preferably less than 6%, and morepreferably from about 2% to 6% by weight.

[0055] Useful polyesters and polyamides include those described in thisapplication below.

[0056] Ionomer is a copolymer of ethylene and an ethylenicallyunsaturated monocarboxylic acid having the carboxylic acid groupspartially neutralized by a metal ion, such as sodium or zinc, preferablyzinc. Useful ionomers include those in which sufficient metal ion ispresent to neutralize from about 15% to about 60% of the acid groups inthe ionomer. The carboxylic acid is preferably “(meth)acrylicacid”—which means acrylic acid and/or methacrylic acid. Useful ionomersinclude those having at least 50 weight % and preferably at least 80weight % ethylene units. Useful ionomers also include those having from1 to 20 weight percent acid units. Useful ionomers are available, forexample, from Dupont Corporation (Wilmington, Del.) under the SURLYNtrademark.

[0057] The sealant layer 28 may have a composition such that any one ofthe above described polymers comprises at least about any of thefollowing weight percent values: 30, 40, 45, 50, 55, 60, 65, 70, 75, 80,85, 90, 95, and 100% by weight of the layer.

[0058] The thickness of the sealant layer is selected to providesufficient material to effect a strong heat seal bond, yet not so thickso as to negatively affect the manufacture (i.e., extrusion) of thesealant film by lowering the melt strength of the film to anunacceptable level. The sealant layer may have a thickness of at leastabout any of the following values: 0.2 mils, 0.25 mils, 0.3 mils, 0.35mils, 0.4 mils, 0.45 mils, 0.5 mils, and 0.6 mils. The sealant layer mayhave a thickness ranging from about 0.05 to about 6 mils, morepreferably from about 0.1 to about 2 mils, and still more preferablyfrom about 0.2 to about 0.5 mils. Further, the thickness of the sealantlayer as a percentage of the total thickness of the sealant film mayrange (in ascending order of preference) from about 1 to about 50percent, from about 5 to about 45 percent, from about 10 to about 45percent, from about 15 to about 40 percent, from about 15 to about 35percent, and from about 15 to about 30 percent. The sealant layer mayhave a thickness relative to the thickness of the sealant film of atleast about any of the following values: 15%, 20%, 30%, 40%, and 50%.

Skin Layer of the Sealant Film

[0059] The skin layer 30 of the sealant film may provide the surfaceupon which a printed image (e.g., printed information) is applied, inwhich case the layer is preferably capable of providing a surface thatis compatible with the selected print ink system. Further, the skinlayer 30 provides the outside surface 26 to which the barrier film 14may be directly laminated, as discussed in more detail below.

[0060] The skin layer 30 may include any of the thermoplastics orcompositions as discussed above in conjunction with the sealant layer28. The skin layer 30 may have a composition or thickness (or both)substantially similar to the sealant layer 28; or, the skin layer 30 mayhave a thickness and/or composition different from the sealant layer 28.For example, the skin layer 30 may comprise one or more polymers havinga melting point higher than the melting point of the lowest meltingpoint polymer of the sealant layer 28 by at least about any of thefollowing values: 3° F., 5° F., 7° F., 10° F., 15° F., 20° F., 25° F.,30° F., and 35° F. The one or more higher melting point polymers of theskin layer may comprise a weight percentage of the skin layer of atleast about any of the following values: 30, 40, 50, 60, 70, 75, 80, 85,90, 95%.

[0061] Further, the one or more polymers of the skin layer 30 having alowest melting point of the polymers of the skin layer may also have amelting point higher than the one or more polymers of the sealant layer38 having a lowest melting point of the polymers of the sealant layer.For example, the lowest melting point polymer of the skin layer may havea melting point higher by at least about any of the following values: 3°F., 5° F., 7° F., 10° F., 15° F., 20° F., 25° F., 30° F., and 35° F.This differential in melting point values generally results in the skinlayer 30 having lower tackiness than the sealant layer 28, since ahigher melting point polymer generally has less tackiness than a lowermelting point polymer. As a result, the manufacture of the sealant filmmay be facilitated, because the sealant film is less likely to stick toitself when wound into a roll—and less likely to cause a reduction inprocessing speeds by sticking to processing equipment.

[0062] The skin layer 30 may include one or more of any of theabove-described polymers, for example, polyamides, polyethylene, and/orpolypropylene, either alone or in combination. The skin layer 30 mayhave a composition such that any one of the above-described polymerscomprises at least about any of the following weight percent values: 30,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100% by weight ofthe layer.

[0063] The skin layer may have a thickness of from about 0.05 to about 5mils, preferably from about 0.2 to about 2 mils, and more preferablyfrom about 0.2 to about 0.5 mils. The thickness of the skin layer mayrange as a percentage of the total thickness of the sealant film of fromabout (in ascending order of preference) 1 to 50 percent, 3 to 45percent, 5 to 40 percent, 7 to 35 percent, and 7 to 30 percent. Usefulthicknesses for the skin layer include at least about any of thefollowing values: 0.1 mils, 0.15 mils, 0.2 mils, and 0.25 mils.

Additional Layers of the Sealant Film

[0064] The sealant film 12 may include one or more additional layers 32,such as a tie, core, or bulk layers. A tie layer is an inner film layerhaving the primary purpose of adhering two layers of a film together.The tie layers, if present in the sealant film, may have the compositionand other attributes as described below in conjunction with the tielayers of barrier film 14. The adjacent layers of a multiple layersealant film 12 may have sufficient compatibility so that a tie layer isnot needed to form a inter-layer bond strength that is sufficientlystrong for the expected end use.

[0065] A core or bulk layer may be an inner film layer having a primarypurpose other than as a barrier or tie layer—for example, serving toprovide a multilayer film with a desired level of strength, modulus, oroptics. A core or bulk layer may include one or more of the polymersand/or have a composition as described above in the Sealant Layersection with respect to the sealant layer.

[0066] Each of the additional layers 32 may have a thickness of fromabout 0.05 to about 5 mils, preferably from about 0.1 to about 2 mils,and more preferably from about 0.2 to about 0.5 mils. The thickness ofan additional layer may range as a percentage of the total thickness ofthe sealant film of from about (in ascending order of preference) 1 to80 percent, 3 to 50 percent, 5 to 40 percent, 7 to 35 percent, and 7 to30 percent. Preferably, adjacent film layers have differentcompositions.

Barrier Film

[0067] The barrier film 14 defines an inside surface 34 and an outsidesurface 36 opposite the inside surface. The outside surface 36 of thebarrier film 14 forms the surface that may engage the heated bar of aheat-sealing device (not shown) used in sealing laminate 10 to supportmember 18, as discussed in more detail below. The outside layer 40 formsthe outside surface 36 of the barrier film.

[0068] The barrier film 14 may have any total thickness as long as itprovides the desired properties (e.g., flexibility, Young's modulus,optics, strength, barrier) for the given packaging application ofexpected use. The barrier film may have a thickness of less than aboutany of the following: 10 mils, 5 mils, 4 mils, 3 mils, 2 mils, 1.5 mils,1.2 mils, and 1.1 mils. The barrier film may also have a thickness of atleast about any of the following: 0.25 mils, 0.3 mils, 0.35 mils, 0.4mils, 0.45 mils, 0.5 mils, 0.6 mils, 0.75 mils, 0.8 mils, 0.9 mils, 1mil, 1.2 mils, 1.4 mils, and 1.5 mils.

[0069] The barrier film 14 preferably has a composition that impartsoxygen barrier attributes to the barrier film. Examples of thecomponents that are useful in imparting decreased oxygen barrierproperties to the film (i.e., “barrier components”) are discussed belowin the Barrier Layer section. If the barrier film 14 is multilayer, thenthe one or more layers of the film that incorporate barrier componentssufficient to decrease the oxygen permeability of the film areconsidered “barrier layers.” If the barrier film is monolayer, then thebarrier components may be incorporated in the sole layer of the barrierfilm, in which case the monolayer barrier film itself would beconsidered the “barrier layer.” In such case, the barrier layer may alsoprovide one or more additional functions, such as the inside, outside(abuse), bulk, and/or core layers of the barrier film. Accordingly, ifthe barrier film 14 is monolayer, then it may have the composition,attributes, and physical characteristics as discussed in conjunctionwith any of the Barrier Layer, Abuse Layer, or Inside Layer sectionsbelow.

[0070] Useful oxygen transmission rates for the barrier film 14 andlaminate 10 are discussed below in the Barrier Layer section.

[0071] The barrier film 14 has a heat-shrinkable attribute. For example,the barrier film 14 may have a free shrink measured at 200° F. in atleast one direction (i.e., machine or transverse direction), in at leasteach of two directions (machine and transverse directions), or a totalfree shrink of at least about any of the following values: 5%, 7%, 10%,15%, 20%, 30%, 40%, 50%, and 60%. Also, barrier film 14 may have a freeshrink measured at 240° F. in at least one direction (machine ortransverse directions), in each of at least two directions (machine andtransverse directions), or a total free shrink measured of at leastabout any of the following values: 7%, 10%, 15%,20%, 25%, 30%, 40%, 50%,55%, 60%, 65%, and 70%.

[0072] The ratio of free shrink of the barrier film 14 to the freeshrink of the sealant film 12, measured at the same temperature and inthe same direction, may be calculated for shrink temperatures of 200° F.and 240° F. in each of the machine and transverse directions. Each ofthe resulting ratios may be at least about any of the following values:0.3, 0.4, 0.5, 0.6, and 0.75—and at most about any of the followingvalues: 3, 2.5, 2, 1.8, and 1.5. It is believed that heat sealing alaminate to a support member (e.g., tray) where the laminate comprisesfirst and second films with free shrinks within these ranges of ratiosreduces the amount and size of wrinkles and/or waves that may otherwiseform in the lid of the resulting sealed package.

[0073] The barrier film 14 comprises one or more polymers forming theoutside surface 36, where the one or more polymers may have a meltingpoint greater than that of the lowest melting point polymer of thesealant layer 28—for example, greater by at least about any of thefollowing values: 25° F., 30° F., 40° F., 50° F., 65° F., 70° F., 80°F., 90° F., and 100° F. Further, outside layer 40 may comprise one ormore polymers having a melting point greater than that of the lowestmelting point polymer of the sealant layer 28—for example, greater by atleast about any of the following values: 25° F., 30° F., 40° F., 50° F.,65° F., 70° F., 80° F., 90° F., and 100° F. The lowest melting pointpolymer of the outside layer 40 may have a melting point higher than thelowest melting point polymer of the sealant layer 28, for example,higher by at least about any of the following values: 25° F., 30° F.,40° F., 50° F., 65° F., 70° F., 80° F., 90° F., and 100° F. The amountof the one or more polymers of the outside layer 40 having either: 1) amelting point greater than that of the lowest melting point polymer ofthe sealant layer 28 or 2) having the lowest melting point of theoutside layer 40 may comprise a weight percentage of the outside layer40 of at least about any of the following values: 40, 50, 60, 70, 75,80, 85, 90, 95%, 100%.

[0074] The barrier or second film 14 is preferably multilayer so thatthe layers in combination impart the desired performance characteristicsto the barrier film. The barrier film 14 may comprise multiple layers,for example 2 layers, from 2 to 15 layers, 3 layers, at least 3 layers,at least 4 layers, at least 5 layers, from 2 to 4 layers, from 2 to 5layers, and from 5 to 9 layers.

[0075] A multilayer barrier film includes: i) an inside layer 38 formingthe inside surface 34 of the barrier film—a layer that upon laminationis proximate the outside layer 26 of the sealant film 12 and ii) anabuse or outside layer 40 forming the outside surface 36 of the barrierfilm 14. The inside layer 38 may be directly adhered to the outsidelayer 40. Alternatively, one or more inner layers 42, such as barrier,tie, core, and bulk layers, may exist between the inside layer 38 andthe outside layer 40. Further, a barrier layer may be directly adheredto outside layer 40. The barrier layer may be a coated barrier layer,that is, a barrier layer formed by coating onto to another layer, forexample, directly coated onto the inside surface of abuse layer 40 or asan exterior layer of the barrier film.

[0076] Below are some examples of layer combinations for the multiplelayer barrier film 14 in which the alphabetical symbols designate theresin layers. Where the multilayer barrier film representation belowincludes the same letter more than once, each occurrence of the lettermay represent the same composition or a different composition within theclass that performs a similar function. E/G, G/F, E/G/F, E/C/G, G/C/F,E/B/G, G/B/F, E/G/C/F, E/C/G/F, E/C/G/C/F, E/C/B/G/B/F, E/C/B/G,G/C/B/F, E/C/B/G/B/C/F

[0077] “B” is a core or bulk layer, as discussed above with respect tothe sealant film.

[0078] “C” is a tie layer, as discussed below.

[0079] “E” is the inside layer of the barrier film, as discussed below.(If “E” is not present, then the first letter represents the insidelayer, for example if “G” is the first letter, then the inside layer isalso a barrier layer. Layer “E” may comprise any of the thermoplasticsor compositions discussed above in the Sealant Layer section.)

[0080] “F” is an outside or abuse layer of the barrier film, asdiscussed below. (If “F” is not present, then the last letter representsthe outside layer, for example if “G” is the last letter, then theoutside, abuse layer is also a barrier layer. Layer “F” may comprise anyof the thermoplastics or compositions discussed above in the SealantLayer section.)

[0081] “G” is a barrier layer, as discussed below.

Barrier Layer of the Barrier Film

[0082] The barrier film 14 may include one or more barrier layers, whichincorporate one or more components (“barrier components”) that markedlydecrease the oxygen transmission rate through the layer and thus thefilm incorporating such layer. Accordingly, the barrier layer of thefilm that is utilized in a lidstock laminate incorporated in a packagemay either help to exclude oxygen from the interior of the package—or tomaintain oxygen within the package.

[0083] Useful barrier components include: ethylene/vinyl alcoholcopolymer (“EVOH”), polyvinyl alcohol (“PVOH”), vinylidene chloridepolymers (“PVdC”), polyalkylene carbonate, polyester (e.g., PET, PEN),polyacrylonitrile (“PAN”), and polyamide.

[0084] EVOH may have an ethylene content of between about 20% and 40%,preferably between about 25% and 35%, more preferably about 32% byweight. EVOH may include saponified or hydrolyzed ethylene/vinyl acetatecopolymers, such as those having a degree of hydrolysis of at least 50%,preferably of at least 85%.

[0085] Vinylidene chloride polymer (“PVdC”) refers to a vinylidenechloride-containing polymer or copolymer—that is, a polymer thatincludes monomer units derived from vinylidene chloride (CH₂═CCl₂) andalso, optionally, monomer units derived from one or more of vinylchloride, styrene, vinyl acetate, acrylonitrile, and C₁-C₁₂ alkyl estersof (meth)acrylic acid (e.g., methyl acrylate, butyl acrylate, methylmethacrylate). As used herein, “(meth)acrylic acid” refers to bothacrylic acid and/or methacrylic acid; and “(meth)acrylate” refers toboth acrylate and methacrylate. Examples of PVdC include one or more ofthe following: vinylidene chloride homopolymer, vinylidenechloride/vinyl chloride copolymer (“VDC/VC”), vinylidene chloride/methylacrylate copolymer, vinylidene chloride/ethyl acrylate copolymer,vinylidene chloride/ethyl methaerylate copolymer, vinylidenechloride/methyl methacrylate copolymer, vinylidene chloride/butylacrylate copolymer, vinylidene chloride/styrene copolymer, vinylidenechloride/acrylonitrile copolymer, and vinylidene chloride/vinyl acetatecopolymer.

[0086] Useful PVdC includes that having between 75 and 95 weight %vinylidene chloride monomer. Useful PVdC includes that having from about5 to about 25 weight %, from about 10 to about 22 weight %, and fromabout 15 to about 20 weight % comonomer with the vinylidene chloridemonomer. Useful PVdC includes that having a weight-average molecularweight (M_(w)) of at least 80,000, such as at least 90,000, at least100,000, at least 111,000, at least 120,000, at least 150,000, and atleast 180,000; and between 80,000 and 180,000, such as between 90,000and 170,000, between 100,000 and 160,000, between 111,000 and 150,000,and between 120,000 and 140,000. Useful PVdC also includes that having aviscosity-average molecular weight (M_(z)) of at least 130,000, such asat least 150,000, at least 170,000, at least 200,000, at least 250,000,and at least 300,000; and between 130,000 and 300,000, such as between150,000 and 270,000, between 170,000 and 250,000, and between 190,000and 240,000.

[0087] A barrier layer that includes PVdC may also include a thermalstabilizer (e.g., a hydrogen chloride scavenger such as epoxidizedsoybean oil) and a lubricating processing aid (e.g., one or moreacrylates).

[0088] Useful polyamides include polyamide 6, polyamide 9, polyamide 10,polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 612,polyamide 6I, polyamide 6T, polyamide 69, copolymers made from any ofthe monomers used to make two or more of the foregoing homopolymers(e.g., copolyamide 6/12, polyamide 12, copolyamide 66/69/6I, copolyamide66/610, copolyamide 6/66, and copolyamide 6/69), and blends of any ofthe foregoing homo- and/or copolymers. Polyamide copolymers include: (a)copolyamide 6/12 comprising (i) caprolactam mer in an amount of fromabout 20 to 80 weight percent (preferably 30 to 70 weight percent, morepreferably 40 to 60 weight percent), and (ii) laurolactam mer in anamount of from about 80 to 20 weight percent; and (b) copolyamide66/69/6I comprising 10 to 50 weight percent hexamethylene adipamide mer(preferably from about 20 to 40 weight percent), 10 to 50 weight percentpolyamide 69 mer (preferably from about 20 to 40 weight percent), and 10to 60 weight percent hexamethylene isophthalamide mer (preferably, fromabout 10 to 40 weight percent).

[0089] Useful polyesters include those described in the Abuse Layersection below.

[0090] A barrier layer preferably has a thickness and compositionsufficient to impart either to barrier film 14 or to laminate 10incorporating the barrier film an oxygen transmission rate of no morethan about any of the following values: 100, 50, 45, 40, 35, 30, 25, 20,15, 10, and 5 cubic centimeters (at standard temperature and pressure)per square meter per day per 1 atmosphere of oxygen pressuredifferential measured at 0% relative humidity and 23° C. All referencesto oxygen transmission rate in this application are measured at theseconditions according to ASTM D-3985. (A reference to the oxygentransmission attributes of a film that is a component of a laminaterefers to the oxygen transmission attributes of the film itself, whichcan be measured by separating the film from the laminate—for example, byusing an appropriate solvent to dissolve the adhesive that bonds thefilms together to form the laminate.)

[0091] A barrier layer may also be formed from a latex emulsion coatinggrade of vinylidene chloride/vinyl chloride copolymer having 5-15% vinylchloride. The coating grade copolymer of vinylidene chloride/vinylchloride may be present in an amount of from 5-100% (of total solids)with the remainder being 2-10% epoxy resin and melt extrusion gradematerial.

[0092] The barrier layer may comprise barrier component in an amount ofat least about any of the following: 50%, 60%, 70%, 80%, 90%, and 100%,based on the weight of the barrier layer. The barrier layer thicknessmay range from about any of the following: about 0.05 to about 6 mils,about 0.05 to about 4 mils, about 0.1 to about 3 mils, and about 0.12 to2 mils.

Abuse Layer of the Barrier Film

[0093] The barrier film 14 may be exposed to environmental stresses, forexample once the barrier film is incorporated into laminate 10 andformed into a package 20. Such environmental stresses include abrasionand other abuse during processing and shipment. The outside or abuselayer 40 preferably provides enhanced resistance to abuse. Since theabuse layer 40 may be directly exposed to the heat seal bar of theheat-sealing equipment (not shown) when forming the sealed package 20,the abuse layer preferably provides heat-resistant characteristics tothe barrier film 14 (and laminate 10) to help prevent “burn-through”during heat sealing. This is because in forming package 20 byconductance heat sealing the laminate 10 to support member 18, sealantlayer 28 is placed in contact with the support member 18, while theoutside layer 40 is proximate the heated bar of the heat sealingapparatus. The heat seal bar transfers heat through the outside layer40, through laminate 10, to the sealant layer 28 to form the heat seal44 between the laminate and support member. Accordingly, outside layer40 may be exposed to the highest temperature during the sealingoperation. Useful melting point attributes for the abuse or outsidelayer 40 have been discussed above.

[0094] The abuse layer 40 may include one or more of any of thefollowing: polyolefins (e.g., polyethylenes, polypropylenes),polyamides, polyesters, polystyrenes, polyurethanes, and polycarbonates.For example, the abuse layer may include any of these polymers in anamount of at least 50 weight %, more preferably at least 70%, still morepreferably at least 90%, and most preferably 100% by weight of thelayer.

[0095] Examples of suitable polyesters include amorphous (co)polyesters,poly(ethylene/terephthalic acid), and poly(ethylene/naphthalate).Poly(ethylene/terephthalic acid) with at least about 75 mole percent,more preferably at least about 80 mole percent, of its mer units derivedfrom terephthalic acid may be preferred.

[0096] Useful polyamides, polyethylenes, and polypropylenes includethose described above.

[0097] The outside layer 40 may have a thickness of from about 0.05 toabout 5 mils, preferably from about 0.3 to about 4 mils, and morepreferably from about 0.5 to about 3.5 mils. The thickness of theoutside layer may range as a percentage of the total thickness of thebarrier film from about (in ascending order of preference) 1 to 50percent, 3 to 45 percent, 5 to 40 percent, 7 to 35 percent, and 7 to 30percent. Useful thicknesses for the outside layer include at least aboutany of the following values: 0.05 mils, 0.1 mils, 0.15 mils, 0.2 mils,0.25 mils, 0.3 mils, 0.35 mils, and 0.4 mils.

Tie Layer of the Barrier Film

[0098] The barrier film 14 may include one or more tie layers, whichhave the primary purpose of improving the adherence of two layers of afilm to each other. Tie layers may include polymers having grafted polargroups so that the polymer is capable of covalently bonding to polarpolymers. Useful polymers for tie layers include ethylene/unsaturatedacid copolymer, ethylene/unsaturated ester copolymer, anhydride-modifiedpolyolefin, polyurethane, and mixtures thereof. Preferred polymers fortie layers include one or more of ethylene/vinyl acetate copolymerhaving a vinyl acetate content of at least 15 weight %, ethylene/methylacrylate copolymer having a methyl acrylate content of at least 20weight %, anhydride-modified ethylene/methyl acrylate copolymer having amethyl acrylate content of at least 20%, and anhydride-modifiedethylene/alpha-olefin copolymer, such as an anhydride grafted LLDPE.

[0099] Modified polymers or anhydride-modified polymers include polymersprepared by copolymerizing an unsaturated carboxylic acid (e.g., maleicacid, fumaric acid), or a derivative such as the anhydride, ester, ormetal salt of the unsaturated carboxylic acid with—or otherwiseincorporating the same into—an olefin homopolymer or copolymer. Thus,anhydride-modified polymers have an anhydride functionality achieved bygrafting or copolymerization.

[0100] The barrier film 14 may also include a tie layer directly adhered(i.e., directly adjacent) to one or both sides of an internal barrierlayer. Further, a tie layer may be directly adhered to the inner(food-side) surface of the outside layer 40. The tie layers are of asufficient thickness to provide the adherence function, as is known inthe art. Each tie layer may be of a substantially similar or a differentcomposition and/or thickness.

Inside Layer of the Barrier Film

[0101] The inside layer 38 of the barrier film 14 may provide thesurface upon which a printed image (e.g., printed information) isapplied, in which case the inside layer is preferably capable ofproviding a surface that is compatible with the selected print inksystem. Further, the inside layer 38 provides the inside surface 34 towhich the sealant film 12 may be directly laminated, as discussed inmore detail below. The inside layer 38 may be a barrier layer.

[0102] The inside layer 38 may include any of the thermoplastics orcompositions as discussed above in conjunction with the sealant layer 28of the sealant film 12. The inside layer 38 may have a thickness of fromabout 0.05 to about 5 mils, preferably from about 0.1 to about 2 mils,and more preferably from about 0.2 to about 0.5 mils. The thickness ofthe inside layer 38 may range as a percentage of the total thickness ofthe barrier film 14 of from about (in ascending order of preference) 1to 50 percent, 3 to 45 percent, 5 to 40 percent, 7 to 35 percent, and 7to 30 percent. Useful thicknesses for the inside layer include at leastabout any of the following values: 0.1 mils, 0.15 mils, 0.2 mils, and0.25 mils.

Bond Strengths of the Sealant and/or Barrier Films

[0103] The term “inter-layer bond strength” as used herein means theamount of force required to separate or delaminate two adjacent filmlayers by adhesive failure, as measured in accordance with ASTM F88-94where the Instron tensile tester crosshead speed is 5 inches per second,using five, 1-inch wide, representative samples. The weakest of theinter-layer bond strength of either or both of the sealant film andbarrier film may be at least about any of the following: 0.2, 0.3, 0.4,0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 pounds/inch.

[0104] The term “intra-layer cohesive strength” as used herein means theamount of force required to separate a film layer by cohesive failure,as measured in a direction that is perpendicular to the plane of thefilm and in accordance with ASTM F88-94 where the Instron tensile testercrosshead speed is 5 inches per second, using five, 1-inch wide,representative samples.

[0105] The term “intra-film cohesive strength” refers to the internalforce with which a film remains intact, as measured in a direction thatis perpendicular to the plane of the film. In a multilayer film,intra-film cohesive strength is provided both by inter-layer adhesion(the adhesive strength between the layers which binds them to oneanother) and by the intra-layer cohesion of each film layer (i.e., thecohesive strength of each of the film layers). In a monolayer film,intra-film cohesive strength is provided only by the intra-layercohesion of the layer which constitutes the film. The weakest of theintra-film cohesive strength of either or both of the sealant film andbarrier film may be at least about any of the following: 1, 1.5, 2, 2.5,3, 3.5, 4, 4.5 pounds/inch.

Additives of Sealant and/or Barrier Films

[0106] One or more layers of the sealant and or barrier films oflaminate 10 may include one or more additives useful in packaging films,such as, antiblocking agents, slip agents, antifog agents, colorants,pigments, dyes, flavorants, antimicrobial agents, meat preservatives,antioxidants, fillers, radiation stabilizers, and antistatic agents.Such additives, and their effective amounts, are known in the art.

[0107] An antifog agent may advantageously be incorporated into sealantlayer 28 or coated onto sealant layer 28, because sealant layer 28 formsthe inside layer adjacent the interior of the sealed package 20. Theincorporation of the antifog agent may occur either before or afterlamination of the barrier film to the sealant film. Suitable antifogagents may fall into classes such as esters of aliphatic alcohols,esters of polyglycol, polyethers, polyhydric alcohols, esters ofpolyhydric aliphatic alcohols, polyethoxylated aromatic alcohols,nonionic ethoxylates, and hydrophilic fatty acid esters. Useful antifogagents include polyoxyethylene, sorbitan monostearate, polyoxyethylenesorbitan monolaurate, polyoxyethylene monopalmitate, polyoxyethylenesorbitan tristearate, polyoxyethylene sorbitan trioleate,poly(oxypropylene), polyethoxylated fatty alcohols, polyoxyethylated4-nonylphenol, polyhydric alcohol, propylene diol, propylene triol, andethylene diol, monoglyceride esters of vegetable oil or animal fat,mono- and/or diglycerides such as glycerol mono- and dioleate, glycerylstearate, monophenyl polyethoxylate, and sorbitan monolaurate. Theantifog agent is incorporated in an amount effective to enhance theantifog performance of the laminate 10.

Optional Energy Treatment of the Sealant and/or Barrier Films

[0108] One or more of the thermoplastic layers of the sealant and/orbarrier films—or at least a portion of the entire sealant and/or barrierfilms—may be cross-linked to improve the strength of the film, improvethe orientation of the film, and help to avoid burn through during heatseal operations. Cross-linking may be achieved by using chemicaladditives or by subjecting one or more film layers to one or moreenergetic radiation treatments—such as ultraviolet, X-ray, gamma ray,beta ray, and high energy electron beam treatment—to inducecross-linking between molecules of the irradiated material. Usefulradiation dosages include at least about any of the following: 5, 7, 10,15, 20, 25, 30, 35, 40, 45, and 50 kGy (kiloGrey). Useful radiationdosages include less than about any of the following: 130, 120, 110,100, 90, 80, and 70 kGy (kiloGrey). Useful radiation dosages include anyof the following ranges: from 5 to 150, from 10 to 130, from 5 to 100,and from 5 to 75 kGy.

[0109] All or a portion of one or two surfaces the sealant film and/orthe barrier film may be corona and/or plasma treated to change thesurface energy of the film, for example, to increase the ability toprint or laminate the film. One type of oxidative surface treatmentinvolves bringing the sealant film into the proximity of an O₂— orN₂-containing gas (e.g., ambient air) which has been ionized. Exemplarytechniques are described in, for example, U.S. Pat. Nos. 4,120,716(Bonet) and 4,879,430 (Hoffinan), which are incorporated herein in theirentirety by reference. The sealant film may be treated to have a surfaceenergy of at least about 0.034 J/m², preferably at least about 0.036J/m², more preferably at least about 0.038 J/m², and most preferably atleast about 0.040 J/m².

Manufacture and Orientation of the Sealant and Barrier Films

[0110] The sealant film 12 and barrier film 14 may each be separatelymanufactured by thermoplastic film-forming processes known in the art(e.g., tubular or blown-film extrusion, coextrusion, extrusion coating,flat or cast film extrusion). A combination of these processes may alsobe employed.

[0111] Each of the sealant film 12 and barrier film 14 may be oriented(i.e., before lamination discussed below) or non-oriented. Either orboth of the sealant film 12 and the barrier film 14 may be oriented ineither the machine (i.e., longitudinal) or the transverse direction, orin both directions (i.e., biaxially oriented), for example, in order toenhance the optics, strength, and durability of the film. Each of thesealant and barrier films may independently be oriented in at least onedirection by one of the following ratios: at least about 2.5:1, fromabout 2.7:1 to about 10:1, at least about 2.8:1, at least about 2.9:1,at least about 3.0:1, at least about 3.1:1, at least about 3.2:1, atleast about 3.3:1, at least about 3.4:1, at least about 3.5:1, at leastabout 3.6:1, and at least about 3.7:1. If it is desired to reduce theheat shrink attribute of a film to a desired level after the film isoriented, then the film may be heat set or annealed after orientation.

Laminate

[0112] Laminate 10 includes sealant film 12 laminated to barrier film 14trapping the printed image 16 between the sealant and barrier films.Inside sealant film 12 and the outside barrier film 14 have free shrinkattributes. The resulting laminate 10 presents a superior appearanceupon sealing to the support member 18 (as described below).

[0113] Laminate 10 also has a heat-shrink attribute which may come intoeffect upon exposure to the elevated temperatures associated withsealing the laminate 10 to the support member. The laminate 10 may haveany of a free shrink in at least one direction (machine or transversedirection), in at least each of two directions (machine and transversedirections), or a total free shrink of at least about any of thefollowing values: 10%, 12%, 14%, 16%, 18%, 20%, and 25% when measured at200° F.; and at least about 21%, 23%, 25%, 30%, 35%, and 40% whenmeasured at 240° F. It is believed that heat sealing a laminate to asupport member (e.g., tray) where the laminate has free shrinks of thesevalues at both 200° F. and 240° F. reduces the amount and size ofwrinkles and/or waves that may otherwise form in the lid of theresulting sealed package.

[0114] If laminate 10 has too much heat-shrink attribute for a givensupport member construction, then the laminate may cause supportstructure 18 to bend, bow, or otherwise distort after exposure to theelevated temperatures associated with sealing the laminate 10 to thesupport member. Laminate 10 may have any of a free shrink in at leastone direction (machine or transverse direction), in at least each of twodirections (machine and transverse directions), or a total free shrinkof less than about any of the following values: 70%, 60%, 50%, 40%, and30% when measured at 200° F.; and less than about 90%, 80%, 70%, 60%,and 50% when measured at 240° F.

[0115] The thickness of the laminate may be less than about any of thefollowing values: 10, 7, 5, 4, 3, 2.8, 2.5, 2.3, 2.2, 2.1, 2, 1.9, 1.8,and 1.7 mils. The oxygen transmission rate attributes of the laminateare discussed in the Barrier Layer section above.

Trap Printed Image

[0116] A printed image 16 is disposed (i.e., trap printed) between thesealant and barrier films at the interface between the outside surface26 of sealant film 12 and the inside surface 34 of the barrier film 14.This may be accomplished by printing one or more images 16 on one orboth of these surfaces before laminating the films together, so thatupon lamination the printed images 16 are “trapped” between the twofilms. For example, the printed image may be “reverse trap printed” byprinting the image onto surface 34 of the barrier film.

[0117] The trapped print 16 is visible through a relatively transparentbarrier film to provide information to the retail purchaser of thepackage. Accordingly, package 10 may be provided with consumer-specificinformation at the time of packaging at a centralized packagingfacility, in the form of a printed image trapped within the laminate 10used at part of the sealed package 20. The availability of trap printedinformation in laminate 10 reduces and potentially eliminates the needfor additional package printing or labeling at the retail distributionpoint. The printed image 16 may include indicia such as productinformation, nutritional information, source identification, and otherinformation, as discussed above. The laminate may include a plurality ofrepeating printed images for each package (i.e., “scatter print”) inwhich registration of the printed laminate 10 with the support member 18is less important—or the printed image may require registration to placethe printed image of the laminate in appropriate alignment with thesupport member 18 before sealing the lidstock to the support member(i.e., “registered print”).

[0118] To form the printed image, one or more layers of ink are printedonto the print surface. The ink is selected to have acceptable inkadhesion, appearance, and heat resistance once printed on the film. Thefilm may be printed by any suitable method, such as rotary screen,gravure, or flexographic techniques. Inks and processes for printing onplastic films are known to those of skill in the art. See, for example,Leach & Pierce, The Printing Ink Manual, (5^(th) ed., Kluwer AcademicPublishers, 1993), which is incorporated herein in its entirety byreference.

[0119] To improve the adhesion of the ink to the surface of the sealantor barrier film, the surface of the sealant or barrier film may betreated or modified before printing. Surface treatments andmodifications include: i) mechanical treatments, such as coronatreatment, plasma treatment, and flame treatment, and ii) primertreatment. Surface treatments and modifications are known to those ofskill in the art. The flame treatment is less desirable for aheat-shrinkable film, since heat may prematurely shrink the film. Theink system should be capable of withstanding without diminishedperformance the temperature ranges to which it will be exposed duringlamination, heat sealing, packaging, and end use.

Appearance Characteristics of the Laminate

[0120] Each of laminate 10 and barrier film 14 may have low hazecharacteristics. Haze is a measurement of the transmitted lightscattered more than 2.5° from the axis of the incident light. Haze ismeasured against the outside surface 36 of the barrier film 40,according to the method of ASTM D 1003, which is incorporated herein inits entirety by reference. All references to “haze” values in thisapplication are by this standard. Preferably, the haze of eitherlaminate 10 or barrier film 14 is no more than about (in ascending orderof preference) 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, and 3%.

[0121] Laminate 10 preferably has a gloss, as measured against theoutside surface 36 of the barrier film 40 of at least about (inascending order of preference) 40%, 50%, 60%, 63%, 65%, 70%, 75%, 80%,85%, 90%, and 95%. These percentages represent the ratio of lightreflected from the sample to the original amount of light striking thesample at the designated angle. All references to “gloss” values in thisapplication are in accordance with ASTM D 2457 (45° angle).

[0122] Preferably, laminate 10 is transparent (at least in thenon-printed regions) so that the packaged food item 22 is visiblethrough the laminate. “Transparent” as used herein means that thematerial transmits incident light with negligible scattering and littleabsorption, enabling objects (e.g., packaged food or print) to be seenclearly through the material under typical unaided viewing conditions(i.e., the expected use conditions of the material). If laminate 10 istransparent then both barrier film 14 and sealant film 12 are alsotransparent. Optionally, barrier film 14 may be transparent whilesealant film is opaque, in which case laminate 10 is opaque while trapprint 16 is still clearly visible through barrier film 14. Preferably,the transparency (i.e., clarity) of any of the laminate 10, sealant film12, and barrier film 14 are at least about any of the following values:65%, 70%, 75%, 80%, 85%, and 90%, as measured in accordance with ASTMD1746.

Modulus of the Laminate

[0123] Laminate 10 preferably exhibits a Young's modulus sufficient towithstand the expected handling and use conditions. Young's modulus maybe measured in accordance with one or more of the following ASTMprocedures: D882; D5026-95a; D4065-89, each of which is incorporatedherein in its entirety by reference. Each of the sealant film 12,barrier film 14, and/or laminate 10 may have a Young's modulus of atleast about any of the following: 70,000, 80,000, 90,000, 100,000,150,000, 200,000, 250,000, 300,000, 350,000 pounds/square inch, measuredat a temperature of 73° F. A higher modulus film has an enhancedstiffness, which may help reduce the tendency of the trap printed image16 to crack when the laminate is flexed. Further, it is helpful thatbarrier film 12 have a high modulus at the elevated temperatures presentwhen the laminate 10 is exposed to heat seal temperatures, for example,during the lidstock sealing process discussed below. Accordingly, theYoung's modulus of the barrier film 14 may be greater than the modulusof the sealant film 12, for example, greater by at least about one ofthe following amounts: 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 75%, 80%,90%, 100%, 125%, 150%, 175%, 200%, 400%, and 600%.

Manufacture of the Laminate

[0124] To manufacture laminate 10, the outside surface 26 of the sealantfilm 12 is placed adjacent to or in contact with the inside surface 34of barrier film 14 so that the films may be bonded together by asuitable lamination technique. Suitable lamination techniques are knownin the art, and include adhesive bonding, reactive surface modification(e.g., corona treatment, flame treatment, or plasma treatment), heattreatment, pressure treatment, heat-welding, and combinations thereof.Suitable lamination methods are described in U.S. Pat. No. 5,779,050issued Jul. 14, 1998 to Kocher et al entitled “Lidded Package Having aTab to Facilitate Peeling,” which is incorporated herein in its entiretyby reference.

[0125] Barrier film 14 may be directly laminated to sealant film 12. Theterm “directly laminated” as used herein means that a first film isbonded to a second film by a suitable lamination method without anadditional film between the first and second films. The first film(e.g., sealant film) may be considered as “directly laminated” to thesecond film (e.g., barrier film)—even if additional material is presentbetween the first and second films—if the additional material is presentprimarily to facilitate the lamination of the first and second films(e.g., an adhesive used in adhesive lamination) or to form part of thetrap print (e.g., a printed image) between the first and second films.

[0126] Laminate 10 has an inter-film bond strength sufficient to survivethe expected packaging and end use conditions without delamination. Theterm “inter-film bond strength” as used herein means the amount of forcerequired to separate or delaminate two directly laminated films, asmeasured in accordance with ASTM F88-94 where the Instron tensile testercrosshead speed is 5 inches per second, using five, 1-inch wide,representative samples. Preferably, the inter-film bond strength betweensealant film 12 and barrier film 14 is at least about any of thefollowing values: 0.5, 0.7, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2, and2.5 pounds/inch.

[0127] As a reactive surface modification lamination method, coronatreatment may be combined with pressure and, optionally, heatimmediately after the corona treatment. The corona treatment providesthe film with a reactively modified surface to enhance laminationbonding. The amount of corona discharge to which the films are exposedis directly proportional to the amount of power supplied to the coronatreatment units, and also indirectly proportional to the speed at whichthe films are passed through the units. In general, corona treatmentunits operate by passing a high voltage electrical current through anelectrode positioned adjacent a film surface to be treated. Theelectrode then produces an electrical discharge which ionizes thesurrounding air to cause reactive surface modification, e.g., oxidation,of the treated film surface.

[0128] Any desired combination of power input to the corona unit andfilm speed may be employed to achieve a desired bond-strength betweenthe films. The amount of power to supplied to the corona treatment unitsmay range, for example, from about 0.02 to about 0.5 kilowatts (kw) perinch of film width. The film speed through the corona treatment unit mayrange, for example, from about 10 to about 2000 feet/minute.

[0129] Alternatively or in addition to a reactive surface modificationlamination method, heat-welding may be employed to laminate the filmstogether. For example, skin layer 30 of sealant film 12 and inside layer38 of barrier film 14 may comprise materials capable of forming aheat-weld bond during lamination. Suitable materials for the interfacinglayers for a heat-weld lamination were discussed above in conjunctionwith the sealant layer of the sealant film. The same or differentthermoplastics may be included in the adjacent film layers.

[0130] In order to facilitate fast and reliable sealing of the lidstocklaminate 10 to the support member, it is preferable that laminate 10 hasgood hot tack attributes. The term “hot tack” is understood to those ofskill in the art. Preferably, laminate 10 has a hot tack strength of atleast 2 Newtons, more preferably at least about 4 Newtons.

Sealed Package

[0131] The lidstock laminate 10 may be heat sealed to support member 18to form sealed package 20.

Support Member

[0132] Support member 18 is a component of package 20 in addition tolaminate 10. Product 22 (e.g., a food product) may be disposed on or insupport member 18. For example, meat products may be disposed in atray-like support member comprising, for example, expanded polystyrenesheet material that has been thermoformed into a desired shape forsupporting the meat product. Product support member 18 preferably is inthe form of a tray having side walls 50 and base 52—which define cavity46 into which the product 22 may be disposed. A peripheral flange 48preferably extends from side walls 50 to provide a sealing surface forattachment of lid 10 to the support member 18 to enclose the product 22within the cavity 46.

[0133] Although the drawings show support member 18 in oneconfiguration, support member 18 may have any desired configuration orshape, such as rectangular, round, or oval. The support member may besubstantially rigid, semi-rigid, or flexible. For example, the supportmember may have a 1% secant flex modulus of at least about any of thefollowing values: 120,000, 140,000, 160,000, 180,000, 200,000, and225,000 pounds/square inch.

[0134] Flange 48 may also have any desired shape or design, such as thesubstantially flat design presenting a single sealing surface as shownin the drawings, or a more elaborate design which presents two or moresealing surfaces, such as the flange configurations disclosed in U.S.Pat. Nos. 5,348,752 and 5,439,132, the disclosures of which areincorporated herein by reference.

[0135] Support member 18 may be formed from any material useful for theexpected end use conditions, including polyvinyl chloride, polyethyleneterephthalate, polystyrene, polyolefins (e.g., high density polyethyleneor polypropylene), paper pulp, nylon, and polyurethane. The supportmember may be foamed or non-foamed as desired. Support member 18 mayhave oxygen transmission barrier attributes, particularly when product22 is an oxygen-sensitive food product. When such oxygen-sensitiveproducts are to be packaged in a modified atmosphere environment toextend either bloom-color life or shelf-life, support member 18preferably has a thickness and composition sufficient to provide anoxygen transmission rate of no more than about any of the followingvalues: 1000, 500, 150, 100, 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5cubic centimeters (at standard temperature and pressure) per squaremeter per day per 1 atmosphere of oxygen pressure differential measuredat 0% relative humidity and 23° C.

[0136] To achieve oxygen barrier attributes, support member 18 maycomprise one or more of the barrier components discussed above in theBarrier Layer section in order to provide oxygen barrier attributes tothe support member. Such barrier components may be incorporated withinstructural sections or aspects of the support member—or optionallyincorporated in a surface layer or film 54 laminated or otherwise bondedto form the inside surface of the support member, as described in U.S.Pat. Nos. 4,847,148 and 4,935,089, and in U.S. Serial No. 08/326,176,filed Oct. 19, 1994 and entitled “Film/Substrate Composite Material”(published as EP 707 955 A1 on Apr. 24, 1996), each of which isincorporated herein in its entirety by reference.

[0137] In addition to (or as an alternative to) providing oxygen barrierattributes, the surface layer or film 54 may enhance the sealability ofthe lidstock laminate 10 to the support member 18. In heat sealinglaminate 10 to the support member 18, layer or film 54 of the supportmember contacts and melds with sealant layer 28 of the sealant film 12to form heat seal 44. To facilitate a strong heat seal 44, layer or film54 may comprise one or more thermoplastics that are compatible with thethermoplastic composition of the sealant layer 28. Accordingly, layer orfilm 54 may comprise any of the polymer compositions and thicknesses asdiscussed in the Sealant Layer and Skin Layer sections regarding sealantfilm 12. The outer surface of layer or film 54 may comprise polymerhaving a melting point or softening point essentially equivalent to orless than that of the polymer forming surface 24 of sealing layer 28,for example, less by about any of the following values: 5° F., 10° F.,15° F., 20° F.

[0138] It was discovered that a strong bond between the laminate 10 andsupport member 18 may be formed where the melting point of the polymerforming the surface of layer 54 is higher than the melting point of thepolymer forming the surface 24 of sealant layer 28—for example, a bondstronger than that formed where the melting point of the polymer formingthe surface of layer 54 was lower than the melting point of the polymerforming the surface of sealant layer 28.

[0139] It is believed that the result of the stronger bond with arelatively higher melting point surface layer 54 was facilitated wherethe melt-flow index of the surface layer 54 was lower than the melt-flowindex of the sealant layer 28 of the sealant film. Accordingly, themelt-flow index of the polymer forming surface layer 54 may be lowerthan the melt-flow index of the polymer forming the surface 24 ofsealant layer 28, for example lower by at least about any of thefollowing values: 0.2, 0.5, 0.7, 1, 1.4, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3,3.5, and 4 g/10 minutes.

[0140] As previously discussed, the sealant layer 28 may comprise one ormore polymers. There is inherently a highest temperature above which themelting point or softening point of at least 70 weight % of the one ormore polymers of the sealant layer exists. Similarly, there are suchhighest temperatures for other such selected weight percentages, such as80, 90, and 100%. The sealing area of the outer surface of the supportmember or layer 54 may comprise any of at least about 70, 80, 90, or 100weight % of one or more polymers each having a melting point orsoftening point at least about any of 3° F., 5° F., 7° F., 10° F., 15°F., 30° F., or 35° F. higher than such highest temperature.

Manufacture of the Sealed Package

[0141] To make sealed package 20, the item to be packaged (e.g., product22) may be placed onto support member 18. Then laminate 10 is placedover the support member so that the sealant film 12 of the laminatecontacts the support member 18. Laminate 10 may be supplied from alarger web of the laminate, for example, from a roll that is unwound tosupply laminate as needed.

[0142] A heated bar or member engages the perimeter of the lid 10corresponding with the perimeter flange 48 of the support member tocompress the lid against the flange of the support member. The resultingheat transfer and compression causes the sealant layer 28 of the lid andsurface layer 54 of the support member to soften and intermix with oneanother. The heat from the sealing operation may also initiate shrinkingof the heat shrinkable laminate to reduce the amount of wrinkles orwaves that may otherwise form in the lid. The excess lid materialextending beyond the flange may be trimmed by a cutting operation.Further, if the laminate is supplied from a roll, portions may besevered from the web after or simultaneously with the heat-welding ofthe laminate to support member 18. Laminate 10 may be severed by aconventional cutting device (e.g., a sharp cutting instrument or athermal cutting device such as a heated wire or heated blade). Theheating bar is removed to allow the sealed area to cool and form asealed bond. A representative process for heat sealing a lid to asupport member is described in U.S. Pat. No. 5,779,050 to Kocher, whichwas previously incorporated by reference.

[0143] The resulting heat-weld or heat-seal 44 preferably extendscontinuously around the upper surface of flange 48 to hermetically sealor enclose product 22 within package 20. In this manner, laminate 10 andsupport member 18 preferably form a substantially gas-impermeableenclosure for product 22 to protect it from contact with the surroundingenvironment including, atmospheric oxygen, dirt, dust, moisture, liquid,and microbial contaminates. Product 22 may be packaged in a modifiedatmosphere where product 22 is oxygen-sensitive (i.e., perishable,degradable, or otherwise changeable in the presence of oxygen) in orderto extend the shelf life or bloom-color life. Such oxygen-sensitiveproducts include fresh red meat products (e.g., beef, veal, lamb, andpork), poultry, fish, and cheese.

[0144] The sealing of the laminate 10 to support member 18 may be by oneor more of the heat sealing methods, including thermal conductancesealing (as described above), impulse sealing, ultrasonic sealing, anddielectric sealing.

[0145] Product 22 is shown as a “low profile” product—that is, a producthaving a maximum height that is below the maximum height of supportmember 18 (i.e., the level at which flange 48 is located). However, a“high profile” product—that is, a product having a maximum height thatis above the maximum height of support member 18—may also be packaged inaccordance with the present invention so that the portion of the productwhich extends above the level of flange 48 will be in contact with lid10.

Seal Strength

[0146] The resulting heat seal bond 44between the laminate 10 and thesupport 18 is sufficiently strong to withstand the expected useconditions. For example, the heat seal bond strength may be at leastabout any of the following values: 0.5, 0.6, 0.7, 0.8, 0.9. 1, 1.3, 1.5,1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, and 8 pound/inch.The term “heat seal bond strength” as used herein means the amount offorce required to separate the sealant layer of the laminate from thesupport member to which the sealant layer has been sealed, as measuredin accordance with ASTM F88-94 where the Instron tensile testercrosshead speed is 5 inches per second, using five, 1-inch wide,representative samples.

[0147] Preferably, the weakest point of any of the inter-layer bondstrength of the sealant film, the inter-layer bond strength of thebarrier film, the intra-layer cohesive strength of the layers of thesealant and barrier films, and the inter-film bond strength is locatedfrom the inside surface 24 of the sealant film by a distance of at leastabout any of the following values: 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1,1.2 mils.

[0148] Further, the resulting sealed packaged also has a seal strengthsufficient to withstand the expected end use conditions, for example, aseal strength of at least about any of the following values: 3, 3.5, 4,4.5, 5, 5.5., 6, 6.5, 7, and 7.5 pounds/inch. The term “seal strength”in conjunction with a sealed package refers to the maximum amount offorce required to cause a cohesive or adhesive failure either withinlaminate that is sealed to the support member, in the bond between thelaminate and the support member of the package, or in the support memberitself, measured in accordance with ASTM F88-94 by pullingrepresentative samples of the film or laminate sealed to the supportmember using an Instron tensile tester with a crosshead speed of 5inches per second and averaging the results from five, 1-inch wide,representative samples. ASTM F88-94 is incorporated herein in itsentirety by reference.

[0149] As used herein, an “adhesive failure” is a failure in which theinterfacial forces (e.g., valence forces or interlocking action or both)holding two surfaces together are overcome. A “cohesive failure” is onein which the molecular attractive forces holding together a layercomposition are overcome.

[0150] Preferably, each of the sealed package 20, laminate 10, and thefilms incorporated in laminate 10 (e.g., sealant film 12 and barrierfilm 14) are non-peelable. The term “non-peelable” used in conjunctionwith a sealed package, laminate, or film means that the seal strengthfailure mode results in a jagged, tattered, or ragged separation—thatis, one that does not cleanly, consistently, or reliably fail in thesame manner and along the same position each time. In this sense, theseal strength failure mode of a non-peelable film or laminate iscontrary to that of a peelable film, which is specifically designed tofail cleanly, consistently, and reliably in the same manner and alongthe same relative position each time, for example by incorporation ofnon-compatible thermoplastics and/or contaminates in two adjacent filmlayers to facilitate peeling and also by incorporating a mechanism suchas a tab to initiate a peel separation, as described in U.S. Pat. No.5,919,547 issued Jul. 6, 1999 to Kocher entitled “Laminate Having aCoextruded, Multilayer Film Which Delaminates and Package MadeTherefrom,” which is incorporated herein in its entirety by reference.

[0151] The following examples are presented for the purpose of furtherillustrating and explaining the present invention and are not to betaken as limiting in any regard.

EXAMPLES

[0152] In the comparatives and examples below, the following materialswere used:

[0153] “Additives” are 5% antifog additives and 2% antiblock additives;

[0154] “Adhesive 1” is a methylene bis(phenyl isocyanate), an ethylester of acetic acid and a polyol curing agent;

[0155] “EPC” is a propylene-ethylene copolymer with 3.3% ethylenecontent and a melting point of 139° C. available from ExxonMobil underthe trademark Escorene PD9302;

[0156] “EVOH1” is an ethylene/vinyl alcohol copolymer having 44 mole %ethylene content, a melt flow index of 1.6, and a melting point of 165°C.;

[0157] “ION” is an ionomer resin modified with nylon available fromDuPont Corporation under the trademark SURLYN AM 7927;

[0158] “LLDPE1” is a heterogeneous ethylene/octene copolymer having amelt-flow index of 1.0 and a density of 0.920 g/cc, available from theDow Chemical Company (Midland, Mich.) under the DOWLEX 2045 trademark;

[0159] “LMDPE” is a heterogeneous ethylene/octene copolymer having anoctene content of 2.5 weight %, a melt-flow index of 2.5, and a densityof 0.935 g/cc, available from the Dow Chemical Company (Midland, Mich.)under the DOWLEX 2037 trademark;

[0160] “MB” is a masterbatch of 90.3% polypropylene homopolymer(ESCORENE PD4062 available from ExxonMobil), 4% inorganic antiblock, and5.7% slip and antiblock agents;

[0161] “MPE” is a homogeneous ethylene/hexene/butene terpolymer having amelt flow index of 2.0 and a density of 0.902 g/cc, available fromExxonMobil Corporation under the EXACT 9103 trademark;

[0162] “Nylon1” is a nylon 6/66 copolymer having a melting point of 196°C.;

[0163] “Nylon2” is a nylon 6/12 copolymer having a melting point of 130°C.; and

[0164] “Tie 1” is an anhydride-grafted LLDPE.

Example 1

[0165] A trap-printed laminate having the composition and constructionshown in Table 1 was formed by adhesively laminating a First Film (i.e.,shrink sealant film) to a Second Film (i.e., shrink barrier film) havinga printed image on its inside surface. The Example 1 laminate had atotal thickness of 1.85 mils. The films used to form the Example 1laminate and the resulting Example 1 laminate itself had the freeshrinks as reported in Table 2. The sealant layer side of the Example 1laminate was heat sealed to a plastic tray (commercially available fromCryovac Inc. under the tradename CS977) to form a sealed package. Thelid of the resulting package was free from visible wrinkles, filmcorrugations, and waves to present a tight, wrinkle-free appearance.TABLE 1 Thickness Film Layer Designation Layer Composition of LayerDesignation (Function) (weight %) (mils) First Film First 93% MPE; 0.2(inside or sealant layer)  7% Additives Second 70% LLDPE1; 0.2 23%LMDPE;  7% Additives Third 50% LLDPE1; 0.5 50% LMDPE Fourth (outside,skin) 70% LLDPE1; 0.1 23% LMDPE;  7% Additives Lamination adhesiveAdhesive1 0.1 Second Film First (skin layer) 95% EPC; 0.2  5% MB Second(tie) Tie1 0.07 Third 80% Nylon1 0.07 (bulk, barrier protection) 20% IONFourth (barrier) 90% EVOH1 0.07 10% Nylon2 Fifth 80% Nylon1 0.07 (bulk,barrier protection) 20% ION Sixth (tie) Tie1 0.07 Seventh (skin layer)95% EPC; 0.2  5% MB

[0166] TABLE 2 Shrink (%) Direction of Example 1 Comparative 1Film/Laminate Shrink 200° F. 240° F. 200° F. 240° F. 1^(st) (sealant)Machine 9 48 9 48 Transverse 18 53 18 53 2^(nd) (barrier) Machine 16 315 16 Transverse 17 34 3 13 Laminate Machine 11 30 8 17 Transverse 16 359 20 Shrink Ratio Machine 1.78 0.65 0.56 0.33 of 2^(nd) Film toTransverse 0.94 0.64 0.17 0.25 1^(st) Film

Comparative 1

[0167] A trap-printed laminate having the composition and constructionshown in Table 3 was formed by adhesively laminating a First Film (i.e.,the same film as used in Example 1) to a Second Film having a printedimage on its inside surface. The Second Film is a biaxially orientedthree-layer coextrusion commercially available from Unitika Ltd. (Osaka,Japan) under the EMBLON E801-15 trademark. The Second Film is 0.6 milsthick and is believed to comprise about 66% nylon and 34% ethylene/vinylalcohol copolymer, as represented in Table 3. The Comparative 1 laminatehad a total thickness of about 1.7 mils. The films used to form theComparative 1 laminate and the resulting laminate had the free shrinksas reported in Table 2. The sealant layer side of the Comparative 1laminate was heat sealed to the same tray as described above for Example1 under the same sealing conditions as Example 1 to form a sealedpackage. The lid of the resulting Comparative package had waves andwrinkles in the form of film corrugations along the sealing edge of thelid at the leading and trailing edges of the package. TABLE 3 ThicknessFilm Layer Designation Layer Composition of Layer Designation (Function)(weight %) (mils) First Film First 93% MPE; 0.2 (inside or sealantlayer)  7% Additives Second 70% LLDPE1; 0.2 23% LMDPE;  7% AdditivesThird 50% LLDPE1; 0.5 50% LMDPE Fourth (outside, skin) 70% LLDPE1; 0.123% LMDPE;  7% Additives Lamination adhesive Adhesive1 0.1 Second FilmFirst (skin layer) polyamide (nylon) Second (barrier) ethylene vinylalcohol Third (skin layer) polyamide (nylon)

[0168] The above descriptions are those of preferred embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theclaims, which are to be interpreted in accordance with the principles ofpatent law, including the doctrine of equivalents. All parts andpercentages are by weight, unless otherwise indicated or well understoodin the art. Except in the claims and the specific examples, or whereotherwise expressly indicated, all numerical quantities in thisdescription indicating amounts of material, reaction conditions, useconditions, molecular weights, and/or number of carbon atoms, and thelike, are to be understood as modified by the word “about” in describingthe broadest scope of the invention. Any reference to an item in thedisclosure or to an element in the claim in the singular using thearticles “a,” “an,” “the,” or “said” is not to be construed as limitingthe item or element to the singular unless expressly so stated. Allreferences to ASTM tests are to the most recent, currently approved, andpublished version of the ASTM test identified, as of the priority filingdate of this application. Each such published ASTM test method isincorporated herein in its entirety by reference.

What is claimed is:
 1. A method of forming a package comprising: a)providing a laminate comprising: a first film having an inside surfaceand an outside surface opposite the inside surface of the first film,the first film comprising a sealant layer forming the inside surface ofthe first film, the sealant layer comprising one or more polymers eachhaving a given melting point, whereby at least one polymer of thesealant layer has the lowest melting point of the one or more polymersin the sealant layer; a second film having an inside surface and anoutside surface opposite the inside surface, the second film comprisingan outside layer forming the outside surface of the second film, theoutside layer comprising at least about 40% by weight of the outsidelayer of one or more relatively high-melt polymers each having a meltingpoint at least about 25° F. higher than the lowest melting point polymerof the sealant layer; and a printed image between the first and secondfilms, wherein: the first film has an oxygen transmission rate greaterthan the oxygen transmission rate of the second film, measured (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C.; the laminate has an oxygen transmission rate of nomore than about 100 cubic centimeters (at standard temperature andpressure) per square meter per day per 1 atmosphere of oxygen pressuredifferential measured at 0% relative humidity and 23° C.; the laminatehas a free shrink in each of the transverse and machine directions of atleast about 10% at 200° F. and at least about 21% at 240° F.; and b)heat sealing the laminate to a support member to form a closed package.2. The method of claim 1 wherein the provided laminate has a free shrinkin the transverse direction of at least about 12% at 200° F. and atleast about 23% at 240° F.
 3. The method of claim 1 wherein the providedlaminate has a free shrink in the transverse direction of at least about14% at 200° F. and at least about 25% at 240° F.
 4. The method of claim1 wherein the provided laminate has a free shrink in the transversedirection of at least about 16% at 200° F. and at least about 30% at240° F.
 5. The method of claim 1 wherein the provided laminate has afree shrink in the machine direction of at least about 11% at 200° F.and at least about 30% at 240° F. and a free shrink in the transversedirection of at least about 16% at 200° F. and at least 35% at 240° F.6. The method of claim 1 wherein the free shrink values of the secondfilm of the provided laminate measured at each of 200° F. and 240° F. ineach of the machine and transverse directions are from about 0.3 toabout 3 times the free shrink values of the first film of the providedlaminate measured at the corresponding temperature and direction.
 7. Themethod of claim 1 wherein the free shrink values of the second film ofthe provided laminate measured at each of 200° F. and 240° F. in each ofthe machine and transverse directions are from about 0.5 to about 3times the free shrink values of the first film of the provided laminatemeasured at the corresponding temperature and direction.
 8. The methodof claim 1 wherein the free shrink values of the second film of theprovided laminate measured at each of 200° F. and 240° F. in each of themachine and transverse directions are from about 0.6 to about 2.5 timesthe free shrink values of the first film of the provided laminatemeasured at the corresponding temperature and direction.
 9. The methodof claim 1 wherein the free shrink values of the second film of theprovided laminate measured at each of 200° F. and 240° F. in each of themachine and transverse directions are from about 0.6 to about 2 timesthe free shrink values of the first film of the provided laminatemeasured at the corresponding temperature and direction.
 10. A packageformed by the method of claim
 1. 11. The method of claim 1 wherein theoutside layer comprises at least about 60% by weight of the outsidelayer of the one or more relatively high-melt polymers.
 12. The methodof claim 1 further comprising placing a food product on the supportmember before heat sealing the laminate to the support member to enclosethe food product in the package.
 13. The method of claim 1 wherein thelaminate has an oxygen transmission rate of no more than about 50 cubiccentimeters (at standard temperature and pressure) per square meter perday per 1 atmosphere of oxygen pressure differential measured at 0%relative humidity and 23° C.
 14. The method of claim 1 wherein thesealant layer comprises at least 30% based on the weight of the sealantlayer of a polymer having a melting point of less than about 115° C. 15.The method of claim 1 wherein the first film is un-perforated.
 16. Themethod of claim 1 wherein the second film has an oxygen transmissionrate of no more than about 30 cubic centimeters (at standard temperatureand pressure) per square meter per day per 1 atmosphere of oxygenpressure differential measured at 0% relative humidity and 23° C. 17.The method of claim 1 wherein the image is printed on the inside surfaceof the second film.
 18. The method of claim 1 wherein the second filmhas a Young's modulus of at least about 150,000 pounds/square inch. 19.The method of claim 1 wherein the thickness of the first film is greaterthan or equal to the thickness of the second film.
 20. The method ofclaim 1 wherein each inter-layer bond strength of the first film of theprovided laminate is at least 2.5 pound/inch.
 21. The method of claim 1wherein the closed package has a seal strength of at least about 5pounds/inch.
 22. The method of claim 1 wherein the closed package has aseal strength of at least about 6 pounds/inch.
 23. The method of claim 1wherein the provided laminate is non-peelable.
 24. The method of claim 1wherein the sealant film of the provided laminate is non-peelable. 25.The method of claim 1 wherein the support member comprises a rigid tray.26. The method of claim 1 wherein the sealant layer of the first film ofthe provided laminate comprises one or more polymers, whereby there is ahighest temperature above which the melting point of at least 70 weight% of the one or more polymers of the sealant layer exists; and thesupport member comprises a sealing area to which the laminate is sealed,the sealing area of the support member comprising at least about 70weight % of one or more polymers each having a melting point at leastabout 3° F. higher than said highest temperature.
 27. The method ofclaim 26 wherein the at least about 70 weight % of one or more polymersof the sealing area each has a melting point at least about 7° F. higherthan said highest temperature.
 28. The method of claim 1 wherein sealingthe laminate to the support member encloses within the package interioroxygen concentration different from that of ambient air.